This invention relates to monitoring apparatus, and more specifically to a novel sensor apparatus for monitoring the passage of discrete articles such as seeds or the like. While features of this invention may be applicable to a variety of uses, the disclousre will be facilitated by addressing the problem of monitoring the passage of seeds as dispensed by a seed planter.
A farmer engaged in mechanized planting of various seeds generally utilizes a seed planter or planting machine pulled behind a tractor. Such a seed planter usually includes apparatus capable of simultaneously planting a plurality of rows of seeds supplied from one or more hoppers. Generally speaking, a plurality of seed delivery tubes or conduits are associated with the seed planting apparatus, one such concuit or seed delivery tube for each row of seeds to be planted. The prior art includes many monitoring devices having seed sensors associated with the individual seed delivery conduits for detecting or monitoring the passage of seeds therethrough. One known especially useful and successful sensor device comprises a light source such as a light emitting diode optically aligned with one or more photosensitive elements such as photoresponsive transistors connected in a circuit so as to emit an electrical signal responsive to momentary changes in the light level incident thereon due to the passage of a seed between the photoresponsive transistor and the light source.
A significant problem which arises with the use of this type of sensor is that dirt and dust on and around the planting equipment may accumulate on or around the sensing components. Thus, the amount of light normally incident upon the photosensitive element in the absence of a seed may be decreased significantly. Such a decrease may result in the change in signal level produced in response to the passing seeds becoming insufficient to energize or signal the following circuit components. Whatever arrangement is chosen for the following circuit some minimum change in the sensor signal input must be chosen and maintained at which the circuit will respond to produce an output signal or indicator of seed passage to indicate the operation of the seed planting apparatus.
In U.S. Pat. No. 3,723,989 to Fathauer et al, a feedback circuit is provided between the output of the photoresponsive element and the light source. This feedback circuit is arranged to increase the current supplied to the light source for increasing the illumination provided thereby in response to a change in the photosensitive element output signal due to the build up of dirt or the like in the light path. Thus, the change in signal output of the photosensitive element responsive to a seed is substantially maintained in the presence of such build up, at least within the capabilities of the light source to increase its output illumination.